Conventionally, as a molding method of an exterior part for providing a decorative effect to a molded product, a method is known in which characters or decorative lines are engraved on a mold surface and embossed on a molded surface, or graining or secondary fabrication after molding is performed. In particular, coloring is generally performed by painting, printing, or sticking on a molded product having a certain color, or special molding such as multicolor molding. However, coloring by these methods uses various pigments or dyes. Such coloring also uses organic solvents or requires post-treatment such as waste liquid treatment. This has increased problems in terms of both operations and the environment.
In response, techniques have been proposed on structural coloring using a physical phenomenon such as the interference or diffraction of light for coloring, instead of so-called coloring matters such as pigments or dyes. For example, there are a technique of alternately laminating two kinds of polymeric substances having different refractive indexes in multiple layers for coloring (for example, see Patent Document 1), a technique related to a fibrous coloring structure body having an alternately laminated structure made up of two kinds of polymeric substances having different refractive indexes (for example, Patent Document 2), and a technique related to a transfer sheet having a minute irregular surface (for example, see Patent Document 3). There is also a technique of forming a diffraction grating structure on a metal for coloring (for example, see Patent Document 4).
<Structural Coloring>
A transfer sheet using structural coloring will be described.
As shown in FIG. 13, a heat-resistant protective layer 42 made primarily of polyamide-imide resin having a glass transition point (Tg) of 250° C. is applied to a surface of a support 41. A diffraction structure forming layer 43 made primarily of urethane resin is applied to a surface of the heat-resistant protective layer 42. Then, a minute irregular pattern forming a diffraction grating is formed on a surface of the diffraction structure forming layer 43 by roll embossing.
Then, a metallic reflective diffraction effect layer 44 is formed on the surface of the diffraction structure forming layer 43 with the minute irregular pattern formed thereon. Further, a heat-resistant mask layer 45 is formed on a surface of the diffraction effect layer 44 by pattern printing. The article having the heat-resistant mask layer 45 formed therein is immersed in a bath containing an NaOH solution, and a portion of the diffraction effect layer 44 exposed from a portion free from the heat-resistant mask layer 45 is etched. Then, an adhesive layer 46 is formed on a surface of the heat-resistant mask layer 45 and a portion of the diffraction structure forming layer 43 exposed by the etching, so as to cover the heat-resistant mask layer 45 and the diffraction effect layer 44. Thus, a transfer sheet 40 is produced.    Patent Document 1: Japanese Patent Laid-Open No. 4-295804    Patent Document 2: Japanese Patent Laid-Open No. 2004-151271    Patent Document 3: Japanese Patent Laid-Open No. 2005-7624    Patent Document 4: National Publication of International Patent Application No. 2006-516108